Cardiac resynchronization therapy (CRT) aims to improve cardiac performance by synchronizing the ventricles. While the term “synchronization” is used, for some patients, a delay between contraction of the right ventricle and the left ventricle may be optimal. Hence, the term synchronization refers more generally to ventricular timing that improves cardiac performance. A general objective measure of lack of synchrony or dyssynchrony is QRS width representative of contraction of both ventricles. For example, a QRS width greater than about 130 ms may indicate dyssynchrony.
CRT can improve a variety of cardiac performance measures including left ventricular mechanical function, cardiac index, decreased pulmonary artery pressures, decrease in myocardial oxygen consumption, decrease in dynamic mitral regurgitation, increase in global ejection fraction, decrease in NYHA class, increased quality of life scores, increased distance covered during a 6-minute walk test, etc. Effects such as reverse modeling may also be seen, for example, three to six months after initiating CRT. Patients that show such improvements are classified as CRT “responders”. However, for a variety of reasons, not all patients respond to CRT. For example, if a left ventricular stimulation lead cannot locate an electrode in a favorable position, then a patient may not respond to CRT.
Often, the ability to respond and the extent of response to CRT depends on an initial set-up of a CRT device in a patient. As described herein, various exemplary technologies aim to improve a clinician's ability to set-up a CRT at implant and to optionally optimize thereafter. In particular, various exemplary techniques include vector metrics based, at least in part, on information acquired from a localization system.